I need to make the best french onion soup possible, please help!

Doing a multi course meal for my mom's 70th birthday, I told her I'd make whatever she asks for and the one thing on the list that I have no experience with is french onion soup.

I've had it a few times but generally don't make or choose soups for myself, whereas she loves and orders it whenever she sees it on a menu. Please give me recipes or tips on how to make one of the best she's ever had!

I also have a smoker and I've been thinking that cold smoking the onions and cheese might be a good addition.